The present invention relates to electrostatic motors. Electrostatic motors rely on the electrostatic force generated between charges. This electrostatic force between charges at rest, as described by Coulomb's law, is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges. Consequently, to create an electrostatic drive using moderate voltages it is important to place the electrodes of an electrostatic motor extremely close together. For example, halving the distance between electrodes increases the electrostatic force between them by a factor of four without increasing the voltage.
The smaller tolerances and distances necessary for electrostatic motors can be realized using micro electromechanical systems (MEMS). MEMS use many of the same processing techniques to achieve similar or equivalent manufacturing tolerances associated with the on-chip or on-wafer tolerances of the semiconductor industry. The MEMS-based electrostatic motors typically takes the form of a moveable element or “mover” and a stationary element or “stator” produced as separate subassemblies using MEMS. As a result, these individual mover and stator elements can be manufactured to exacting specifications.
However, individual MEMS components are often assembled together using more traditional and less accurate manufacturing processes. In the case of electrostatic motors, these less accurate manufacturing processes do not inherently provide the necessary tolerance required to place the mover and stator elements in a proper position for reliable electrostatic motor operation. Accordingly, the precision assembly of MEMS components used in electrostatic motors and other devices requires advanced manufacturing techniques to make them function and operate reliably over time.
Improving traditional manufacturing techniques is becoming even more important as high-density storage devices specify use of MEMS-based electrostatic motors. In one particular design, a linear electrostatic motor using MEMS mover and stator assemblies is responsible for accurately driving a platform supporting a storage medium. An atomically sharp needle in a fixed position writes and reads the storage medium by depositing and sensing extremely small charges on the storage medium. The needle both stores and reads large amounts of information as the aforementioned MEMS components in the linear electrostatic motor control very small movements of the platform holding the storage medium. Unfortunately, the larger tolerances associated with traditional manufacturing affects both the storage capacity and reliability of the resulting high-density storage device driven by a linear electrostatic motor with MEMS mover and stator.
After manufacture, it is also important for these high-density storage devices to maintain a certain alignment or registration between the platform holding the storage medium and the various MEMS assemblies in the motor. If this registration cannot be maintained, the data transfer to and from the drive may be interrupted or result directly in data loss. This is particularly important when these high-density storage devices are used in portable electronic devices such as still cameras, motion cameras, personal digital appliances, cell phones and music players as normal use often includes substantial “g-shock” type accelerations that increase the potential for losing registration. Clearly, the usefulness of high-density storage devices using MEMS technology depends on the ability of these devices to maintain registration in light of the shock and vibration.
In particular, the linear electrostatic motor must be able to contend with both lateral and normal shock to the platform holding the storage medium. One problem is a lateral shock in the plane of the storage medium can be stronger than the electrostatic forces holding the storage medium platform in registration. If the lateral shock is strong enough, the shock can cause the platform to “skitter” relative to the atomic needle thus losing registration and possibly data.
Another problem concerns the shock normal to the plane of the storage medium. Typically, the platform supporting the storage medium is held in place by the restorative force of tiny flexures. Flexures include a variety of forms, often including beam-like structures arranged in a “zigzag” pattern. A shock normal to the storage plane drives the movable platform and its electrodes towards the stationary electrodes associated with the platform's supporting frame. As a result, the normal force combined with the electrostatic force of the linear motor can overcome the restorative force of the flexures and causes the platform to be pulled rapidly towards the stationary electrodes also resulting in data loss.
In light of the aforementioned problems, it is desirable to have robust high-density storage systems and electrostatic motors that can endure physical shocks and continue operating.
Like reference numbers and designations in the various drawings indicate like elements.